Method of treating aqueous iodide solutions

ABSTRACT

A method is provided for removing iodide from aqueous solutions in which the iodide is converted to iodine. The porous granules of the polyvalent metal chelating resin containing zirconium peroxide bound to the chelating groups thereof is contacted with the aqueous iodide solution. The iodine is formed within the granules and retained therein, permitting the aqueous solution to be separated to create iodine. This iodine can be recovered by organic solvent elution. The oxidative capacity of the resin granules has been reduced, it can be regenerated after removal of the obtained iodine by contacting the resin granules with aqueous hydrogen peroxide.

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/187,176, filed Jan. 25, 1994, now U.S. Pat. No. 5,367,031.

FIELD OF INVENTION

The field of this invention is the removal of iodide from water. Theinvention is particularly concerned with water treating substances whichadsorb or convert iodide in drinking water. The invention also hasapplication in the production of iodine from iodide-containingbrine-well waters.

BACKGROUND OF INVENTION

When halogen had been used to disinfect water, it has been proposed toscavenge the residual halogen by a secondary resin treatment. Forexample, as disclosed is U.S. Pat. No. 3,316,173, water may be treatedwith bromine released from a strong base anion exchange resin. Thebromine eluted from the resin in the treated water can be scavenged asdescribed in U.S. Pat. No. 3,462,363 through use of a scavenger resin intandem with the bromine-providing resin.

It is known that peroxides of polyvalent metals such as zirconium,titanium, lanthanium, and thorium can oxidize iodide in aqueous solutionto elemental iodine: Gantz and Lambert, J. Phys. Chem. (1957)61:112-113. These authors reported that zirconium peroxide can be formedfrom zirconyl ion attached to filter paper or starch. Zirconyl ionsolutions were found to react irreversibly with cellulose. It washypothesized that this was the result of the attachment of the zirconylion through hydroxy groups of the glucose units. After attachment of thezirconyl ions, treatment of the filter paper with hydrogen peroxideproduced zirconyl peroxide which remained attached to the paper.

SUMMARY OF INVENTION

This invention is based in part on the discovery of a novel watertreating resin which is capable of oxidizing iodide to iodine and alsoof retaining the formed iodine. The composition comprises porousgranules of a metal chelating resin which provide functional groupscapable of binding polyvalent metal ions. The granules are prepared sothat they contain strongly bonded zirconium peroxide. When watercontaining iodide is contacted with the resin, iodide is oxidized withinthe granules to form iodine. The iodine thus formed tends to be retainedwithin the granules. Treated water can be produced which is essentiallyfree of both iodide and iodine.

This invention also involves a method of treating water with theoxidizing resin described above. This method can be used for treatingwater which has been disinfected by being contacted with a polyiodideanion exchange resin, which results in the release of iodide ions in thetreated water. The iodide-containing water is contacted with thezirconium peroxide containing chelated resin granules. The oxidizingaction of the zirconium peroxide converts the iodide to iodine which isretained within the granules. By separation of the treated water fromthe granules, disinfected water is produced which is free of both iodideand iodine.

In preferred embodiments of the oxidizing resin of this invention, thezirconium is so strongly held that it can be repeatedly regeneratedwhile remaining attached to the resin. The oxidative capacity of theresin can be restored by treating the resin with hydrogen peroxide,thereby making it possible to repeatedly regenerate the resin after itsoxidizing capacity has been exhausted. This is an important andsurprising feature of the present invention. In another application ofthe present invention, low concentrations of iodide in brine waters canbe converted to iodine which becomes trapped in the resin matrix. Uponbecoming saturated with the iodine, it can be eluted by an organicsolvent such as acetone.

DETAILED DISCLOSURE

To prepare the zirconium peroxide-containing resin of this invention, apolyvalent metal ion chelating resin is employed. For example, agel-type or macroporous-type chelating resin containingalkylaminophosphonic chelating groups can be used. Bio-Rad Laboratories,Richmond, Calif. sells chelating resins which are polystyrene divinylbenzene copolymers containing iminodiacetic acid functional groups.These resins are identified as "Chelex 20" (macroporous form) and"Chelex 100" (gel form). The gel form of the Chelex resin is preferredfor the purposes of this invention. Chelex 100 is available inanalytical and biotechnology grades which are suitable for use in thisinvention. Chelex 20 is a technical grade resin which can also be used.Other metal-chelating resins which bind multi-valent metal cations aredescribed in U.S. Pat. No. 4,895,905. The resins may contain differentchelating functionalities. For purpose of the present invention, thechelating resins preferably contain iminodiacetic acid functionalgroups.

A suitable reagent for use in preparing the resin is zirconyl chloride,which is available commercially in hydrate form, such as zirconylchloride heptahydrate or octahydrate. The zirconyl chloride hydrates aresoluble in water and partially soluble in alcohols such as methanol.With either the alcohol or aqueous method, it has been found importantto first convert the dissolved zirconyl chloride to zirconium peroxidebefore contacting the solution with the chelating resin. This sequenceproduces a much more oxidative product. The desired sequence is incontrast to the previously described procedure of Gantz and Lambert(1957), cited above, in which the zirconium ion is bonded to filterpaper or starch and thereafter converted to the peroxide. That procedurehas not been found to be satisfactory for preparing the zirconium resinof this invention.

For example, an alcohol solution (or dispersion) of zirconyl chloride isprepared. Next hydrogen peroxide is added to produce a solution ofzirconyl peroxide. That solution is then applied to the resin granulesto form the oxidative resin. Methanol is the preferred solvent but otherlower alcohols can be used, such as ethanol or isopropanol. Usingmethanol tends to somewhat improve the oxidative capacity of the resin.

In the alcohol solution procedure, a chelating resin, such as Chelex 20or Chelex 100, is prepared by being suspended in the same lower alcohol,such as anhydrous methanol. The resin can be washed several times withthe anhydrous alcohol to remove any water present. During thispretreatment, the resin granules will shrink. When the zirconyl chloridehydrate is suspended in the anhydrous alcohol, complete solution may notoccur, the zirconyl chloride being partially in the form of adispersion. When the hydrogen peroxide is added to the zirconyl chloridehydrate-alcohol suspension, reaction heat is generated and completesolution will usually occur. This can be visualized by the clearing ofthe cloudy suspension. The resulting solution of zirconyl peroxide isadded to the alcohol suspension of the Chelex resin. This results inswelling of the resin granules. To assure completeness of reaction,these reactants may be mixed for 0.5 to 1.5 hours. The resin granulesmay then be allowed to settle out of the treating solution. Thesupernatant solution can be poured off, and the resin can be purified byrepeated washing with distilled water. During such water washing, theresin granules will again shrink in volume.

With the preferred procedure as described, it appears that the gelmatrix of the resin granules is maintained. When an aqueous treatingprocedure is used, however, it appears that the gel matrix partiallycollapses. This inhibits the most efficient binding of the zirconylperoxide to the iminodiacetate groups. An oxidizing resin prepared bythe aqueous method has substantially less oxidative capacity than theresin prepared by impregnation with a methanol solution of zirconylperoxide.

Zirconium peroxide chelating resins prepared as described can be usedfor treating water containing iodide salts. On being contacted with thebound zirconium peroxide within the resin granules, the iodide ions areconverted to iodine. As this conversion proceeds, the formed iodine islargely retained within the granules. This can be observed by a changeof color of the granules.

An alternate use of the resin of this invention is to produce iodine.The iodine collected within the resin granules can be removed by asuitable elution procedure. In a primary proposed application, however,the zirconium peroxide-containing chelating resin is used as secondarytreatment for drinking water, which has been contacted with a polyiodidedisinfecting resin. Even if the polyiodide resin is used in conjunctionwith an iodine scavenging material, such as granulated activated carbon,or an anion exchange resin, over time these iodine scavenging materialswill tend to reduce iodine to iodide, and thus result in an iodideresidual in the treated water. By subsequently treating the water withthe zirconium peroxide resin of this invention, both iodide and iodinecan be effectively removed. This invention in one of its embodiments cantherefore be used as a combination treatment.

Polyiodide anion exchange resins for use in this combination treatmentcan be prepared in accordance with known procedures, and commerciallyavailable strong base anion exchange resins can be used. Such resins areavailable in the form of granules or beads prepared for ion exchangeuse, and are typically provided in a chloride or sulfate form. The resinis commonly obtained or converted to the chloride form and thenconverted to a polyiodide form. Quaternary ammonium anion exchangeresins are preferred, such as those described in U.S. Pat. No.4,999,190. However, other strong base anion exchange resins can beemployed such as tertiary sulfonium resins, quaternary phosphoniumresins, and alkylpyridinium resins.

The strong base anion exchange resin in the chloride form can be treatedwith a solution of potassium triiodide, as described in U.S. Pat. No.3,817,860, to produce a triiodide resin. Triiodide and pentaiodideresins, containing primarily triiodide can be prepared as described inU.S. Pat. No. 4,137,183. Other polyiodide resins containing selectedamounts of triiodide, pentaiodide or higher polyiodides can be preparedas described in U.S. Pat. No. 4,238,477. Preferably, the polyiodideresin is prepared as described in U.S. Pat. No. 4,999,190. Such resinscontain more than fifty percent pentaiodide (I₅ ⁻) together with alesser proportion of triiodide (I₃ ⁻). In preferred embodiments, aquaternary ammonium anion exchange resin is prepared containing morethan sixty percent pentaiodide. The exact procedure for producing thiskind of resin is set out in U.S. Pat. No. 4,999,190, and that procedureis incorporated herein by reference.

The present invention is further illustrated in preferred embodiments bythe following examples.

EXAMPLE I Preparation of Zirconium Peroxide Resin

The zirconium peroxide resin can be efficiently prepared in thefollowing manner. A commercially available iminodiacetate resin ineither the gel or macroporous form (100 ml; 0.40 meq per ml; Chelex 20or Chelex 100) is suspended in anhydrous methanol and washed severaltimes with anhydrous methanol to remove water. During this resuspensionof the volume of the resin shrinks to approximately 35 ml. In anothercontainer zirconyl chloride heptahydrate (12.5 gm) is suspended inanhydrous methanol (100 ml.). Complete solution does not occur and thesuspension remains cloudy. hydrogen peroxide (30%, 20 ml.) is added tothe zirconyl chloride heptahydrate-methanol suspension to produce thezirconyl peroxide. During this reaction heat is liberated and completesolution occurs as visualized by clearing of the cloudy suspension. Thezirconyl peroxide in 120 ml. volume is then added to the settled Chelexresin bed and mixed. After this addition the resin volume swells toabout 80 ml. The reactants are occasionally mixed on a rotary shaker for1 hr. The resin bed is allowed to settle and the fluid portion pouredoff. The resin is then repeatedly washed with distilled water. Duringthis washing the settled resin volume again shrinks to about 50 ml.

EXAMPLE II Determination of Properties of Zirconium Peroxide Resin

Several experiments were conducted to study the iodide oxidationcharacteristics of the zirconium peroxide resin and its ability toretain the oxidation product, elemental iodine. In all cases theseexperiments pertain to the zirconium peroxide resin prepared using themethanol procedure described in Example I. In these experiments,typically, a solution of potassium iodide at a given concentration isprepared and allowed to flow through a bed of the zirconium peroxideresin. The iodide and iodine concentrations of the input solution andeffluent are measured using an iodide-selective electrode and acommercially available (Hach) DPD reagent, respectively. The generalresult is that iodide is substantially oxidized to iodine but verylittle iodine is released to solution. This iodine is retained in thegel matrix and can be observed to accumulate as the gel matrix changescolor from a clear white to dark reddish-brown characteristic ofelemental iodine. Representative data are set out below:

    ______________________________________                                             Iodide Conc.                                                                             Iodide Conc.                                                                             Iodine Conc.                                                                           Iodine Conc.                                   mg/l (ppm) mg/l (ppm) mg/l (ppm)                                                                             mg/l (ppm)                                Trial                                                                              Input      Output     Input    Output                                    ______________________________________                                        1    1270       127        0.0      1.5                                       2    12.7       <0.127     0.0      0.0                                       3    1.27       <0.00127   0.0      0.0                                       ______________________________________                                    

These data show that in the case of trial 1 where 1,270 ppm of iodidewas oxidized to 1,143 ppm iodine (1,270-127) only 1.5 ppm was containedin the resin eluate. This dramatically demonstrates the iodine capturingmechanism of the resin. Even at very low iodide concentrations, trials 2and 3 respectively, there is significant iodide oxidizing capability. Inthese cases no iodine could be demonstrated in the eluates because itsconcentration and efficiency of capture in the resin was too great.

EXAMPLE III Regeneration of Zirconium Peroxide Resin

A fifty ml lot of zirconium peroxide resin was placed in a graduatedcylinder with a ground glass stopper. Approximately 50 ml of KI solution(0.10M) was added to the resin. Very quickly the iodide solution wasoxidized to molecular iodine as evidence by a dramatic color change inboth the resin bed and the aqueous supernatant. Both phases turned thecolor of a concentrated iodine solution.

The aqueous supernatant fluid was poured into an evaporating dish andthe resin bed repeatedly (5 times) washed with acetone (25 ml aliquots).These acetone washes were also added to the same evaporating dish. Thepooled aqueous-acetone washes tested strongly for oxidative iodine withcadmium iodide-linear starch reagent. After repeated washing the resinreverted to a pale yellow color, indicating substantial removal of theelemental iodine.

The resin was repeatedly washed with 50 ml aliquots of distilled water.The final wash was aspirated leaving only the 50 ml resin bed. To thisresin was added 25 ml of 30% hydrogen peroxide (H₂ O₂). During thesubsequent 10 minutes evidence of chemical reaction was apparent asthere was evolution of gas and some warming of the reaction mixture.Excess hydrogen peroxide was decanted and the resin again repeatedlywashed with distilled water. Again, a KI solution (0.10M) was added tothis resin and again there was strong evidence for oxidation of the KIsolution to elemental iodine. Acetone washing again was repeated toextract iodine from the resin bed.

The foregoing regeneration procedure has been found repeatable for atleast four regenerations. This finding leads to the followingconclusions: 1) zirconium is strongly held to the Chelex 100 resin bedso that it survives and can function as a reversible oxidant on demandwhen converted to the zirconium peroxide form; and 2) while theoxidative capacity of a given quantity of zirconium peroxide resin canbe exhausted by the addition of a suitable amount of an oxidizablespecies i.e. iodide (I⁻), this oxidative capacity can be restored bytreating the resin with hydrogen peroxide.

We claim:
 1. Method of treating an aqueous solution containing iodide,comprising contacting said solution with porous granules composed of apolyvalent metal chelating resin having zirconium peroxide bound to thechelating groups thereof, said contacting oxidizes the iodide in saidsolution to iodine, separating the solution from the granules whereinthe resulting iodine is retained within said granules after theseparation.
 2. Method of claim 1 in which said granules containiminodiacetate polyvalent metal chelating groups.
 3. The method ofclaims 1 or 2 in which the resin granules containing said iodine arecontacted with an eluting solution for removal of the iodine, andthereafter said granules are contacted with aqueous hydrogen peroxide toregenerate the oxidizing capacity of the resin granules.
 4. The methodof preparing iodine from an aqueous solution containing iodide,comprising contacting said solution with porous granules composed of apolyvalent metal chelating resin having zirconium peroxide bound to thechelating groups thereof, said contacting oxidizes iodide to iodine,separating the solution from the granules while leaving the iodinewithin said granules, and thereafter recovering the iodine from saidgranules by solvent elution.
 5. The method of claim 4 in which saidgranules contain iminodiacetate polyvalent metal chelating groups.